The Role of Oxidized Organic Compounds in Urban New Particle Formation

LEE TISZENKEL, James Flynn, Shanhu Lee, The University of Alabama in Huntsville

     Abstract Number: 401
     Working Group: Urban Aerosols

Abstract
New particle formation (NPF) takes place frequently in polluted urban areas worldwide, impacting human health, air quality and climate. Past studies have proposed that urban NPF takes place via clustering of sulfuric acid with base species with a possible contribution by oxidized organic compounds. However, the exact mechanisms of urban NPF are poorly understood due to a lack of comprehensive measurements of NPF precursors at urban sites. We have made a comprehensive chemical analysis of NPF at a highly populated and polluted urban site in Houston, Texas. We measured gas-phase sulfuric acid, ammonia, amines, and oxidized organic compounds with three chemical ionization mass spectrometers (CIMS). Using the Filter Inlet for Gases and Aerosols (FIGAERO) we measured organic compounds both in the gas- and particle-phase, enabling the analysis of ambient gas-phase organic compounds as well as organic compounds that partition in to the particle phase. These measurements of gas-phase precursors and particle chemical composition were coupled with particle size distributions down to critical cluster diameters. We found that the presence of oxidized organic compounds is a critical criterion for NPF initiation in the urban atmosphere. Additionally, we found that the relatively lower ratio of organonitrates in Houston represents a distinct chemical environment that distinguishes the participation of organics in urban Houston NPF from other highly polluted areas such as Chinese megacities. Our observations for the first time give closure to both nucleation and growth rates with the measured sulfuric acid, base, and low-volatility highly oxygenated organic molecules. With rapidly growing urban heat islands and enhanced urban emissions, this multicomponent NPF process will play an increasingly more important role globally in the changing climate.